Mesh and LOD

[Ryker Silvercloud]

Hello

I have a problem with mesh objects that keeps bothering me - as maker and shopper as well  - and it seems like a mysterious the more I focus on it.

I`ll try to demonstrate the problem through a series of pictures. All snapshots were taken at LOD 4.

Image #1

Here you have a couch I`ve made in Blender and uploaded to SL.
The base frame and cushions are 2 objects exported unjoined as a linkset dae. The two throw pillows are 2 meshes saved and uploaded as 1 object.
I did not custom made any LOD models. The lowest LOD was set to zero and physics set to lowest. As you can see it holds it shape across the sandbox at Mauve.

Image #2

Panel #1
Here you have the same couch. I`ve added a chair, a coffee table and a rug. The grid is made by 10x10 meters unlinked prims (not mesh).
I am standing about 20 meters away from the seating group. Notice the brick wall to the right.
(The coffee table has actually dropped down to the medium level at this distance. It`s only to be expected and tells me that the LODs are behaving correctly at this state.)

Panel #2
I walk over behind the brick wall.

Panel #3
Here I step out from behind the wall and walk up to the same place where I started. Now the cushions and the throw pillows have dropped to the lowest LOD depsite I have returned to the same state as in panel #1. I did not touch the camera during this exercise.
The cushion and pillows will stay like this as long I stand still - like stuck at the lowest level - however, and here comes the mystery, I can trigger the LODs to switch to a higher level by either walking forwards or backwards - even pulling my camera back !

Panel #4
In the last panel I`ve pulled the camera back to upgrade the LOD and now the couch looks right - but notice the camera is farther away than in panel #3 . That`s the thing I don`t understand.

I see this issue in my own mesh builds - foremost cushions and pillows - but now and then I see the same thing occure at other home furnishing stores around SL.

I use the LL Viewer (see details at the bottom) and have experimented with different settings but nothing seems to help. Nor does the issue seem to depend on how I set my LOD factor. The same problem occurs at LOD 2, LOD 4 and even LOD 6

Last week I started to read back on almost anything I could find about the mesh uploader and LOD in this forum. Depsite I have gained a lot of other useful information on how to optimze my mesh I haven`t found any explanation to this specific problem.

To be exact:
1. What happened to the couch while I was behind that wall ?
2. How come the the cushions won't upgrade when I walk up to exact the same place as where I started ?
3. How come you can trigger the LOD to switch to a higher level by walking backwards or simple pulling your camera back ?

I greatly appreciate any suggestion on this problem.

Thank you for reading my post

===============

Details:
I use the SL Viewer version 5.0.4.325124
Internet Speed Test: Download 85.7 Mbit / Upload 47,62 Mbit

Draw distance: 128m
Bandwidth: 500kbit/s
LOD factor: 4
Render quality: 2 / 7
Advanced Lighting Model: Disabled

Computer:
CPU: Intel(R) Core(TM) i7-4700HQ CPU @ 2.40GHz (2394.45 MHz)
Memory: 12172 MB
OS Version: Microsoft Windows 8 64-bit  (Build 9200) compatibility mode. real ver: 10.0 (Build 10586)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: GeForce GT 750M/PCIe/SSE2

Info Couch

Image #1

 

 

Image #2

[arton Rotaru]

That you have to move the cam in one way or the other to force loading the proper LOD is something I have experienced since day one of mesh as well. Since I am a heavy Ctrl+Alt cammer anyway, I got quite used to it.

I guess what happens when you walk behind the wall, is that the occluded objects got culled, and when you walk back the objects load the Lowest LOD first again. You could try to temporary disable Object-Object Occlusion (Crtl+Shift+O) to check if the culling is part of the problem

Creating custom LODs will make that less of a problem, because there would be still something to see. You could then also drop your LOD factor setting and may be able to set your Graphics quality to something higher than 2.

[Klytyna]

Stop using the "One Graphics Slider to Ruin them All" and start using the 'Advanced settings, that way you don't end up with the standard SL default settings of "see more but it looks crap"...

[Chic Aeon]

Well first of all you did a  FANTASTIC job explain with pictures and all the info one could want. So many gold stars (kudos) there.

This does seem to be a newish issue and it has been talked about here on the forums before but briefly with no solution. Edit: I was talking about the BLACK breakup that you see on photo #3.

Since I am wondering if this is a graphics card issue I am going to paste my specs in here:

CPU: Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz (3298.07 MHz)
Memory: 16286 MB
OS Version: Microsoft Windows 10 64-bit (Build 14393)
Graphics Card Vendor: NVIDIA Corporation
Graphics Card: GeForce GTX 980/PCIe/SSE2

Windows Graphics Driver Version: 21.21.0013.7653
OpenGL Version: 4.5.0 NVIDIA 376.53

Edit: I use the Firestorm viewer. 

I noticed this the first time a couple of months ago and it was on a couch "I" had made :D. The same areas that appear black in yours appeared black in mine. My couch was lower poly with higher LOD settings than yours. I thought it might be the texture as mine couch pieces didn't (don't as it still happens now and then) break up with the LODS like yours, it simply lost the texture and became all black.  

Uploading a new texture didn't help and then I started noticing the same issue on certain prim parts of the house I had moved into (not mine but made by a very competent mesh maker so unlikely a mesh issue itself. As I type I see arton has posted on this. Ah technology and the new forums.

Anyway it seems like this is with us for awhile. I had never see the issue before. And I see that arton is talking about the LOD settings and I am concerned with that big black mass LOL.    

I would like to encourage you to change your LOD settings down to 2 at least. Many to most folks have them set there because they just use the defaults or they cannot turn them up to 4 because of computer issues. The world is VERY different looking at 2 or below and it is good to see how your mesh appears to others. 

There are some long threads on LODs (one from around last Christmas as I was working on things for Advent) that might be helpful so far as how to upload (not the black issue).

I am still seeing the black areas now and then and actually that doesn't seem to be an LOD issue as I am close to both couch  and pillars in the walls of the house. So I have no clue about that. 

I am not a custom LOD maker as my efforts in that (and likely the box modeling style I use) haven't shown that it is an advantage for me. I DO however test at low LOD settings (and leave mine at 2 now). But just in general I try and make my items hold their shape at a much further distance than is necessary - at LOD2. 

Edit: I agree with arton that this is a typical "problem". I also cam in and out (often halfway across a sim) and seldom move. So I would consider THAT part of your experience normal --- not that it helps if it frustrates you. 

Edited May 12, 2017 by Chic Aeon
adding info

[ChinRey]

The basic answer is that even if you try to deactivate the LoD system by increasing the LoD factor, your computer still has to find time to process all that data and the higher you set the LoD factor, the harder it'll have to work.

When a object enters or re-enters the view, it is first rendered as a basic prim shape, then at the lowest LoD and upwards until it reaches the LoD level it's suppsoed to have. Usually this happens so fast you don't notice it but if the computer is too busy, it may take a while. Sometimes the process can even time out so you're stuck at a too low LoD level and the only solution is to force a reload the way Arton and Chic suggested.

Reading your computer specs I suspect it is a cpu rather than a gpu issue in your case but the solution the same anyway: make proper LoD models and set your graphics prefs to something your computer can safely handle.

[Ryker Silvercloud]

Thank you, everyone, for your quick replies and good answers. I really appreciate it .

arton Rotaru .....I can`t believe it, I think you have fixed the problem ! I have now disabled Object-Object Occlusion as you suggested and right now testing inside SL. So far everything looks fine. I`m so amazed. I`m 9 hrs ahead of SL and it`s getting late here, however, I`ll run a few more tests tomorrow - visit some stores to see how things look with this setting. Then I`ll come back and tell you more...for now, thank you so much

Klytyna, I`m not sure I understand your comment. My default graphics is High+ but I`ve always set it to Mid and from Avanced Settings I`ve unchecked Atmospheric shaders, Avanced Lightning Model and a few other changes that I don`t recall right no. Thanks anyway.

Chic Aeon, thank you for your comments and the kudos
I think arton Rotaru came up with the right solution, but now I have the chance I would like to thank you for your excellent turtorials and the encouragement and optimism you always convey in your posts and comments.
I actually learned how to "cheat on the lowest" some months ago from one of your older posts (Posted April 12, 2013). I know you have moved beyond that point and now making mesh for LOD 2 . I was over and to visit your inworld store a week ago and lowered my LOD to 2, and was impressed how pretty and well things are designed over there.

As for that black mass.....do not worry, here`s at least something I can explain. You see, the couch is two objects: cushions and base frame and each object has their backed textures. So when I backed the AO for the base frame I left the seat - and back cushion in the couch - actually they go slightly down into base frame and leave this dark area. The same with the pilllows - backing the AO map for the back cushions I left the pillows in the couch. You can see in this snapshot that the dark spots are the areas that are hidden by the pillows and thecushion. However, when the the pillows and cushions collapse, the black areas become visible and that surely doesn`t look pretty.

ChinRey, thank you for your reply. The information you share on how an object is rendered first as a basic prim and move upwards till it reaches the LOD level it`s supposed to have is very interesting. And I think you explain it so well "Sometimes the process can even time out so you're stuck at a too low LoD level"  - that`s exactly how I felt was happening. "stuck at a too low LOD level" - that`s really good way to describe it.  

 

[Chic Aeon]

2 hours ago, Ryker Silvercloud said:

As for that black mass.....do not worry, here`s at least something I can explain

Ahhhh. Well hopefully you will never have "my" black mass issue as it is NOT a dark bake behind my pillows LOL; there are no pillows .  

And yes, our early thoughts (and sometimes tutorials) stay with us and can at times haunt us. We all hopefully keep learning and get better. 

Today I found a way to make a very convincing pillow. I knew it was too high polly for our needs (and it IS) but I have also learned along the way -- some trial and error and some from other's comments including things here on this forum (LOTS on this forum when I was just starting) and so tomorrow I can take that "so not game asset" method and make it work for SL. 

 

Your couch is quite lovely by the way!  Glad your issues are fixed. There are times happily when it really isn't "US"!  Hallelujah.

[ChinRey]

52 minutes ago, Ryker Silvercloud said:

ChinRey, thank you for your reply. The information you share on how an object is rendered first as a basic prim and move upwards till it reaches the LOD level it`s supposed to have is very interesting. And I think you explain it so well "Sometimes the process can even time out so you're stuck at a too low LoD level"  - that`s exactly how I felt was happening. "stuck at a too low LOD level" - that`s really good way to describe it.  

 

Yw.

I think I'm going to follow up with a little bit (or maybe rather a big bit) of some basics that too few builders and users in Second Life seem to be aware of.

A scene in Second Life is consists of big and small triangles. The ground of a sim is made from 131072 triangles, the sky is displayed on a screen made from several hundred triangles (and yes, that's far more than is actually necessary), each prim can have anything from eight (I think) to 1024 triangles, each sculpt has aproximately 1000 (exact numebr depends on stitching type), a mesh can have up to 174,752 of them (but fortunately it usually has far less). The bare system avatar has about 7000 triangles, add a fitted mesh body and mesh hands and feet and a few other "essential" attachments and we're talking several hunded thousand triangles for each avatar.

It's very rare for a scene to have less than a milion triangles and it's not unsual with several millions of them. Ideally we want that scene to be redrawn 40 times a second or more and definitely not less than about 20. There is no computer in the world that can manage that.

Fortunately the viewer has several mechanisms to simplify the scene. Objects outside the camera's view can be omited of course, that helps a lot. Objects hidden behind other objects are culled. That means the computer has to figure out exactly which objects are hidden - a bit of work but still well worth the effort. Objects that are 100% transparent are safe to ignore. Draw distance eliminates objects that are far away - hardly ideal but necessary. Second Life's culling mechanisms are rather crude and inefficient by modern standards but most of the time they do the job well enough.

LoD is one of those culling mechanisms, it's the system the viewer uses to eliminate details that would have been too small to be noticeable anyway. By increasing the LoD factor, you bypass that mechanism, adding suprefluous triangles all over the scene. How many depends on several factors. In some scenes icnreasign the LoD factor hardly adds anything at all, but often doubling the LoD factor increases the number of active triangles by 20, 30, 40, even 50%.

Unless the scene has some special complicating factors, any computer in Second Life should be able to handle 200,000 active triangles without too much problems. A good game computer should be able to handle 500,000, maybe even more. But the moment you're pushing the graphics processor beyond its comfort zone, its performance starts to drop at an accelrating rate and you don't have to overload it very much before you get serous problems with render failures (like the ones this thread started with) and/or frame rate dropping down to almost a standstill.

Then there are those complicating factors.

The graphics processor saves a lot of time and effort by reuising data from oen frame to the next. That's easy enough for things that don't move around very much but flexible triangles - the system avatar, fitted mesh and fleixprims - just won't stand still and their size, rotation position and shape have to be recalculated all the time. If I rememebr correctly, the render cost formula stipulates that a fitted mesh triangles add 1.2 times as much load as a static one. I think the actual number is a bit higher but in any case it's a significant load increase.

Of course, the triangles has to be colored too, not just drawn. The graphics processor ahs to combine the data from the texture, from the various shaders, from the normals and from any extra surface maps the object may have to determine exactly what color each and every pixel on the screen should have. Some very rough numbers based on some very rough tests (if anybody have better data, please let us know!): 200-400 pixels worth of regular texture or specular map or 300-500 pixels of alpha texture or normal map equal one mesh triangle in terms or raw render load. But please note that these are very rough figures and also that there are a number of factors that may increase texture induced render load a lot. (For reference, a 1024x1024 texture has about a million pixels, a 512x512 a quarter of a million and a 256x256 65,536. You can do the rest of the math yourself )

Yes, I know that was a long lesson and a complicated one too even though I simplified it a lot. It is an important one though. You don't necessarily need to remember all those numbers but a basic understanding of what the poor graphics processor has to do and what can give it problems is eccential for anybody who wants to build efficient content for a virtual reality.

Now, back to the start. In my first post I wrote that it might be the cpu, not the gpu that was causing problems in this case. The reason was that the scene seemed so simple. Even if the funriture was so overloaded with polys it would have looked solid in wireframe view, there still didn't seem to be enough triangles and textures to cause any gpu any serious problems. But I may have been wrong because I forgot taht there is an avatar in the picture and it's one that looks like it may have quite a lot of fitted mesh attached. Remember I said a mesh avatar can have several hundred thousand triangles? and that flexible triangles are harder on the gpu than static ones? With LoD factor 4 you force the gpu to handle pretty much everything ther at full LoD and although we need more testing to say for sure, there is some evidence that some of the other culling mechanisms are less effective for avatar attachments than for rezzed objects. I don't know for sure but I wouldn't actually rule out the possibility that the avatar alone puts so much laod ont he gpu it has problems handling the rest of the scene. It may be possible way to test that theory by switching Advaned Lighting Mode on and see if that fixes the render failure. Yes, I know that sounds illogical but try it if you want to.

[Chic Aeon]

I wanted to add something to this thread even though it is in theory "done" (always a good thing). 

I have always traveled between two worlds -- that is SL and RL and out there in 37654B *wink*. I DO try and pass on what I have learned and I am happy that folks are listening  -- especially when I am correct. I have never (crosses fingers and hopes this is true but thinks it is) said that I do things the BEST way. I know I don't.  I DO however TEST up a STORM which means that while I seldom make my own LODs I do test to see what folks are seeing. It helps that most of my mesh is pretty darn low poly to start with (not always but most often). 

I do FREQUENTLY use the "zeroed out" lowest LOD setting for my mesh. That being said I also TEST (test - test - test) to see how that is working. Do I need to see a book halfway across a sim -- nope, I do not. 

That's my choice and my position and I am sticking with it. I build for LOD 2 folks (sometimes down below that, now and then at 3 when I really want something that looks fantastic and isn't "practical" for SL). I really do not care (yes, cold hearted) about the people using the very lowest LOD settings. If I went that route, that would be unfair to the folks that do have great machines, have spent money to get them and that LIVE HERE (like me). That likely doesn't make sense to some folks, but it is my choice. 

So never think that I believe I am doing the very best that I could. I have made compromise, but they have been intentional. I believe that all creators have a right to make choices. I don't always applaud them all, but I do recognize their right TO their choices.

And with that I am FINALLY getting off for the day. Wine in hand I go forward to Netflix .....

 

 

[ChinRey]

19 minutes ago, Chic Aeon said:

 have always traveled between two worlds -- that is SL and RL

I've heard abut this RL thing. Is it any good?

[Chic Aeon]

1 hour ago, ChinRey said:

I've heard abut this RL thing. Is it any good?

LOL. Now and then it has it moments. I have to admit it has been awhile though :D. 

That made me smile. Thanks.

[Chic Aeon]

@Ryker Silvercloud I have been known to be a bit dense at times ^^.   I woke up this morning and realized that your "black blob area" issue WAS my black blob area issue and that the cushions (very plain) of my couch were not loading === the same apparently with the pillars in my house. What is very odd about that as both are very low poly with high LOD upload settings and they didn't always have that issue.  So either something changed on the server or on my computer. BUT mystery is solved, so THANK YOU!    :D.

[arton Rotaru]

18 hours ago, Ryker Silvercloud said:

arton Rotaru .....I can`t believe it, I think you have fixed the problem ! I have now disabled Object-Object Occlusion as you suggested and right now testing inside SL. So far everything looks fine. I`m so amazed. I`m 9 hrs ahead of SL and it`s getting late here, however, I`ll run a few more tests tomorrow - visit some stores to see how things look with this setting. Then I`ll come back and tell you more...for now, thank you so much

Good, now we know what's going on. Though, I wouldn't recommend to disable Object-Object Occlusion permanently. I had added the word temporary on purpose actually. I would rather live with forcing the LODs by moving the cam, rather than take the performance hit from non-culled hidden objects.

[Ryker Silvercloud]

Sorry for the late response

Chic, I don`t know if the issue you experienced this morning is the same as I see. When I uploaded Image# 2 it was 1600x1600 px and you could better see that the 2 pillows and the 4 cushions had collapsed to two single triangles. However, I see that the image has been scaled down during upload and it`s not so clear what`s happening in panel #3 - I don`t know if it was me who did something wrong while I added the picture - that part was actually a bit tricky.

Anyway, I`m glad you solve the mystery

Talking about photos and the many good treads in this forum, it`s a pitty so many images are missing. I believe, I only see 10-15 % of them and sometimes they show something else than what is refererred to in the text. I do, however, see all the photos that has been posted recently (within the last six months or so).

As for changing LOD setting down to 2. It`s something I`ve never really thought about till I started to read back in the mesh forum. I think mine has been at 4 since the sculptie days - those days people would pass out notecards telling you to raise you LOD setting to 4 or 6 - sometimes even higher - and I just left it at 4. If I change my graphics settings for taken pictures it will switch down to the default and then I reset it back to 4.  It`s just what I was being told.

Now of course I`ll pay attention to this in the future and gradually lower it.

 

ChinRey, thank you for your detailed lesson on basic graphics processing. You not only uncover useful information about the culling mechanisms in SL, but also personally, it helps me to improve and expand my vocabulary on this topic. English isn`t my native language and sometimes I struggle to get the words right and how to explain these rather complicated topics.

Yes, there`s an avatar in the snapshot. I used my own avatar as a kind of cursor to indicate that the distance from the camera to the couch is the same in panel #1 as in panel #3. During this excersise my camera was just hanging there somewhere above my shoulder.
I doubt the avatar and the fitted mesh clothes have any influence on this specific issue - the way I remember I have tested without avatar in the photo - but I`ll test this when I get back to SL Sunday.

As for the culling mechanisms and Object-Object Oclusion; it`s something I haven`t heard about, before arton Rotaru mentioned it in his first reply. I googled it and basically there`s not much info about it. However, I did find a few things in the former SLUniverse Forums and Nalates Urriah mention it in a post called Second Life Performance Boost and links back to a thread in the SL Forum.

So I don`t if is good or bad to leave the Object-Object Oclusion unticked - if it improves or slows down your performing in general. In my case it has solved the problem with objects that fall apart when I cam around and then cam back to my avatar. My couchions and pillows don`t collapse when I turn my back to the couch
and I`m not "stuck at a too low LoD level" as ChinRey mention. I`ve also seen a significant improvement when I walk around in different furniture stores: there is a better flow because things don`t have to reload when I cam around -  I guess.

In any case I`ve found more relief; so I`ll probably leave Object-Object Oclusion disabled for a while till I find a more sustainable solution.

arton Rotaru, I`m stilled amased you could identify the problem so fast and that it was related to the culling mechanisms   thanks again

 

 

Edited May 13, 2017 by Ryker Silvercloud

[ChinRey]

1 hour ago, Ryker Silvercloud said:

So I don`t if is good or bad to leave the Object-Object Oclusion unticked - if it improves or slows down your performing in general.

Obejct-Object Occlusion is that culling mechanism I mentioned that objects hidden behind other objects. Disabling it helps in a case like the one you had here since the furniture is never removed from the scen and don't have to be reloaded. But keeping track of all hidden objects can add a lot of work for the poor comuter so, as Arton said, you don't really want to do it as a permanent solution.